1. Field of the invention
The present invention relates to a rotary jack assembly for lifting and rotating a quayside crane use din a wharf to change the travel of the crane.
2. Description of the Prior Ar
As shown in FIG. 4, a crane runs on a rails 10a extending along one side of a wharf and rails along the other side of the wharf. Surrounded by the rails 10a and 10b is a circular rail 10c on which a conventional jack assembly runs. The jack assembly is intended to lift and rotate the crane to change its travel, from the rails 10a to the rails 10b and vice versa. The jack assembly generally includes a rotary frame assembly 1, 2 having frames 1, 1, 2 and 2, frame receiving members 3, wheel frames 4 provided under the frame receiving members 3 to rotatably support wheels, and a plurality of crane supporting arms 5 assembled in the respective frame receiving members 3 to extend out of and retreat into the frame assembly. The crane generally includes a right and left sill 7, 7, a plurality of legs 8, and a plurality of wheels 9. In the drawing, reference numeral 11 denotes a rail reversal unit. Reference numerals 12 and 13 denote stoppers.
Specifically, a vertical cylindrical housing 15 is fitted in each frame receiving member 3 of the rotary frame assembly and is connected to the wheel frame 4 by a pin 19 as shown in FIG. 5(B). A hydraulic cylinder 14 is arranged vertically in the cylindrical housing 15 and has a piston rod 14a connected to the frame receiving member 3 by a pin. Each crane supporting arm 5 is slidably arranged in the frame receiving member 3 and has a bifurcated portion 5a at its base in an attempt to avoid the cylindrical shaft 15. A hydraulic cylinder 17 is mounted in the frame 1 and has a piston rod 17a connected to the bifurcated portion 5a. With this arrangement, the hydraulic cylinderes 17 are operated to move the crane supporting arms 5 out of the frames 1, 2 to thereby position them under the right and left sill 7, 7 of the crane. The hydraulic cylinders 14 are then operated to raise the frame assembly 1, 2 together with the frame receiving mbmers 3 and the crane supporting arms 5 whereby the crane is lifted via the sills 7, 7. Reference numeral 20 denotes pads.
The travel of the crane is changed as follows:
The crane first runs on the rails 10a in a direction as indicated by the arrow as shown in FIG. 4. The crane stops when the wheels come into engagement with the stoppers 12 and is located above the jack assembly.
Next, the hydraulic cylinders 17 are operated to move the crane supporting arms 5 out of the frames 1, 2 and to thereby position them under the right and left sill 7, 7 (see FIG.5). The hydraulic cylinders 14 are then operated to raise the crane supporting arms 5 together with the frame assembly 1, 2 and the frame receiving members 3. Hereby the crane is lifted via the right and left sill 7, 7 (see FIG&gt;6). In this state, the jack assembly and the crane are rotated approximately 90.degree.. Thereafter, the hydraulic cylinders 14 are operated to lower the frame assembly together with the crane supporting arms 5. The hydraulic cylinders 17 are then operated to retreat the crane supporting arms 5 into the interior of the frames 1, 2. The crane is now located on the rails 10b and runs in a direction as indicated by the arrow . The crane can be moved back to the rails 10a from the rails 10b by reversing the forgoing operation.
In such a conventional rotary jack assembly, however, each crane supporting arm 5 must be bifurcated as at 5a at its base so as to avoid the cylindrical shafat 15 in the frame receiving member 3 and to allow sliding movement of the crane supporting arm 5 in the frame 1. However, this results in an increase in the width and size of the frame receiving members (3). Thus, the crane supporting arms become complicated and unstable. In the case that the height of the sills is low, lifting of the crane may not be smoothly effected because the height of the crane supporting arms can not be lowered.